Disappearing-reappearing radar chaff and method for production

ABSTRACT

Dispersable radar chaff having the characteristic of intermittently being electrically reflective and non-reflective, and comprising an inert core element progressively surrounded by alternated layers of reducable metallic salt, resin permeable material and oxidizeable metal, the chaff so formed being activated before dispersion by application of an oxidizingreducing agent, said agent in progressively working its way inward alternately oxidizing a metallic layer to become nonreflective, and reducing a metallic salt layer to become reflective.

United States Patent Fiedier Apr. 3, 1973 54] DlSAPPEARlNG-REAPPEARINGFOREIGN PATENTS OR APPLICATIONS RADAR CHAFF AND METHOD FOR PRODUCTIONWilliam S. Fiedler, Madison, Wis.

The United States of America as represented by the Secretary of th AirForce Dec. 27, 1962 inventor:

Assignee:

Filed:

Appl. No.:

U.S. Cl ..343/l8 E, 343/18 B Int. Cl ..G0ls 7/42 Field of Search..343/l8 B Reierences Cited UNITED STATES PATENTS l2/l970 Turner et al...343/18 B 6/1970 Miller ..343/l8 B RESIN PERMEABLE MATERlALELECTRICALLY CONDUCTIVE MATERIAL 63 9,740 7/1950 Great Britain......343/l8 B Primary ExaminerBenjamin A. Borchelt AssistantExaminer-N. Moskowitz Attorney-Wade Koontz and Louis E. Hay

ABSTRACT Dispersable radar chaff having the characteristic ofintermittently being electrically reflective and nonreflective, andcomprising an inert core element progressively surrounded by alternatedlayers of reducable metallic salt, resin permeable material andoxidizeable metal, the chaff so formed being activated before dispersionby application of an oxidizing-reducing agent, said agent inprogressively working its way inward alternately oxidizing a metalliclayer to become n0n-reflective, and reducing a metallic. salt layer tobecome reflective.

8 Claims, 2 Drawing Figures RESIN PERMEABLE COMPOUND MATERIALELECTRICALLY NON-CONDUCTIVE MATERIAL REDUCIBLE SILVER COMPOUNDELECTRICALLY CONDUCTIVE MATERIAL PATENTEDAPRB 191a RESIN PERMEABLEMATERIAL COMBINED OXlDlZlNG-REDUCING AGENT INVENTOR. WILL/AM 5. F/EDLERflg ag v TTORNE Y5 DISAPPEARlNG-REAPPEARING RADAR CHAFF AND METHOD FORPRODUCTION This invention is directed in general to the field of radarchaff and, more particularly, to the method of utilizing chemicalcompounds to produce chaff whose reflective characteristics may be madeto disappear and reappear at intervals.

Radar chaff, which is generally composed of relatively short filamentsof conductive fibers, is used to deceive or confuse ground radarinstallations and render them ineffective. Because of electricalconductivity, each filament of chaff acts as a dipole which registersupon the radar screen and produces a deceptive reading. When suchfilaments become nonconductive as by deactivation, the radar apparatuswill not detect the chaff. Hence, by alternately deactivating andreactivating the chaff, a reading is produced on the radar screen whichresembles a moving target, or a target which is detected and lost. Suchoperation, to say the least, causes great confusion.

it has been found that disappearing-reappearing chaff, as contemplatedby this invention, may be produced by applying on fiber glass or plasticsuch as polyethylene terephalate separate coatings or layersof reduciblemetallic salt and oxidizable metal; and then applying a liquid solutionor dispersion containing a chemical which will first oxidize themetallic coating and then reduce the coating containing the reduciblemetallic salt. in this manner, a chaff is produced that will giveintermittent readings on a radar screen due to its ability to becomefirst nonconductive due to the oxidation of the outer conductive metalcoating and then conductive due to the reduction of the metallic salt.

An object of this invention is to produce radar chaff which isintermittently conductive and nonconductive.

A further object of this invention is to provide radar chaff havingcontrolled intervals for being conductive or nonconductive.

Another object of this invention is to provide a radar chaff which willproduce a reading on a radar screen which is similar to the reading froma moving object.

The invention is further illustrated by the following examples whichillustrate certain embodiments but are not to be taken as limiting theinvention only to the embodiments shown, it being understood that otherembodiments and equivalents will be apparent to those skilled in the artafter the following description and drawings in which:

FIG. 1 is a schematic drawing in partial section of chaff ascontemplated by this invention, and

FIG. 2 is the chaff shown on FIG. 1, which, prior to dispersion into theatmosphere, is treated with a chemical solution to produce theintermittent disappearingreappearing effect.

The radar chaff of this invention, referred to generally as chaff 10,may comprise as its inner or core layer 12 any suitable electricallynonconductive material such as fiber glass, thermoplastic orthermosetting resins such as mylar, nylon, dacron, orlon, rayon, etc.;paper and natural fibers such as wool, cotton, silk or line. Anymaterial may be selected in either filament or sheet form providing suchmaterial is electrically nonconductive.

Applied to core 12, as hereinafter described, is a first coating orlayer of a reducible silver compound 14 such as silver nitrate, silvernitrite, silver chloride, silver bromide, silver fluoride, 'or silveriodide. This coating may be applied by any suitable coating techniquefor obtaining a thin layer of relatively uniform thickness such as bybrushing, spraying or dipping. Preferably, it is applied by usingstandard coating equipment such as a knife coater, reverse roll coater,or the like. It is particularly suitable to coat with a transfer rolldipping into a pan of coating material and having the other side of theroll contacting the core material. After passing over the roll, the webis then passed over a Mayer equalizer rodconsisting of a rod of aboutone quarter inch diameter wound with wire in the form of a tight coil orhelix, the wire being of the order of No. 6 wire.

The reducible silver salt 14 is an electrically nonconductive layer.Upon treatment with a reducing agent, the silver salt is reduced tometallic silver which is electrically conductive to thus make the chaffconductive.

Applied to the outside of the layer of silver salt 14 is a first layerof resin permeable material 16. The layer of silver salt 14 will remainnonconductive for a predetermined period depending upon the thicknessand the material used as the resin permeable coating 16. In this manner,the chaff is rendered nonconductive and no reading is recorded on theradar screen until the reducing agent penetrates through the resinpermeable material and into contact with the silver salt. By selectionof a suitable resin permeable material, and by controlling the thicknesswith which applied, the time of appearance after the reducing agentreaches the surface of the resin permeable material is controlled. Thisresin permeable layer 16 may be made from the common semi-permeablematerials such as gelatin, colloidal silica, or sodium silicate, tomention a few. The resin permeable layer may be applied by any of theconventional coating procedures above mentioned.

A layer of electrically conductive material 18 is next placed over thesemi-permeable resin coating 16. This metallic layer provides theinitial electrical conductivity of the chaff, permitting the chafi togive readings on the radar screen. Any metallic metal may be used as themetallic layer, as for example: aluminum, magnesium, copper, silver andzinc. The characteristic of the metal is such that it can be deactivatedor rendered nonconductive when attached by a suitable oxidizing agent.'The electrically conductive material 18 may be applied on the resinpermeable material 16 by any conventional coating procedure. The rate ofthe initial disappearance of the chaff from detection on the radarscreen may be controlled by the thickness of the metallic layer. This istrue since the chaff will disappear ini-' tially from the radar screenwhen the metallic layer is rendered nonconductive due to it oxidation bythe oxidizing and reducing agent.

Although chaff in accordance with this invention may be produced withoutsuch final layer, the rate of initial disappearance of the chaff fromdetection may be further controlled by applying another coating 20 ofthe semi-permeable material heretofore mentioned upon the layer ofconductive metal. This layer will provide a time delay before theoxidizing and reducing agent reaches the metallic layer and renders thechaff nonconductive. v

The chaff produced by the above described procedure is made to disappearand reappear on the radar screen by the chemical action of a combinedoxidizing-reducing agent 22 shown Upon reaching the metallic layer, thereading given by the chaff will disappear since the metallic layer willbe rendered nonconductive by oxidation to its salt. After penetratingthrough the metallic layer, the agent penetrates through permeable layer16 and into the layer 14 of silver salt. After contacting the silversalt, the agent will reduce the silver salt to conductive silver causingthe chaff to be reactivated and rendered conductive, to again producereadings on the radar screen.

An oxidizing-reducing agent 22 may be prepared of a strong base such aspotassium hydroxide or sodium hydroxide together with sodiumhyposulfite. The mixture may be in the form of a liquid dissolved in anyconventional solvent such as alcohol or other volatile low freezingsolvent, and applied to the chaff before the chaff is dropped from anairplane or dispersed into the air by other means. The solvents alsoprevent the sticking together of individual pieces of chaff which wouldotherwise normally occur in the presence of moisture. By regulating theamount of sodium hyposulphite in the solution, the rate of reduction ofthe silver salt layer may be increased or decreased as desired. Thisprovides a means of regulating the time of reappearance of the chaffafter disappearance. Potassium nitrate may be added in like manner toincrease the rate at which the metallic layer oxidizes. By increasing ordecreasing the amount of potassium nitrate, the rate of oxidation may beincreased or decreased as desired.

From the above disclosure, it is obvious that disappearing-reappearingchaff may be made using any number of layers; within limits, of thematerials disclosed. Likewise, that the order of disappearance andreappearance may be reversed by changing the order of application on thecore, or by adding an additional silver salt layer to the outside of thechaff illustrated. Hence, the disclosure should be taken in anillustrative rather than in a limiting sense; and it is the desire andintention to reserve all modifications within the scope of the appendedclaims.

I claim:

1. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of metallic salt about said core, one or morecoaxial layers of metallic material alternately spaced with said layersof metallic salt, said metallic salt being reducible by said agent andsaid metallic material being oxidizable by said agent, and a coaxiallayer of permeable material between each layer of metallic salt andmetallic material.

2. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of metallic salt about said core, one or morecoaxial layers of metallic material alternatly spaced with said layersof metallic salt, said metallic salt being reducible by said agent andsaid metallic material being oxidizable by said agent, and a pluralityof coaxial layers of permeable material one of which is between eachlayer of metallic salt and metallic material and one of which forms theouter layer of the chaff so formed.

3. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of metallic salt about said core and having theinner layer joined to said core, one or more coaxial layers of metallicmaterial alternately spaced with said layers of metallic salt, saidmetallic salt being reducible by said agent and said metallic materialbeing oxidizable by said agent, and a plurality of coaxial layers ofpermeable material one of which is between each layer of metallic saltand metallic material and one of which forms the outer layer of thechaff so formed.

4. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of silver salt about said core, one or morecoaxial layers of metallic material alternately spaced with said layersof silver salt, said silver salt being reducible by said agent and saidmetallic material being oxidizable by said agent, and a plurality ofcoaxial layers of resin permeable material one of which is between eachlayer of silver salt and metallic material and one of which forms theouter layer of the chaff so formed.

5. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of silver salt about said core and having theinner layer joined to said core, one or more coaxial layers of metallicmaterial alternately spaced with said layers of silver salt, said silversalt being reducible by said agent and said metallic material beingoxidizable by said agent, and a plurality of coaxial layers of resinpermeable material one of which is between each layer of silver salt andmetallic material and one of which forms the outer layer of the chaff soformed.

6. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing'agent and comprising: an electrically inert filamentcore, a layer of silver salt coaxial with and joined to the surface ofsaid core, a first coaxial layer of resin permeable material joined tothe surface of said layer of silver salt, a coaxial layer of metallicmaterial joined to the surface of said first layer of resin permeablematerial, and a second coaxial layer of resin permeable material joinedto the surface of said layer of. metallic material, said silver saltbeing reducible by said agent and said metallic material beingoxidizable by said agent.

7. The method of producing disappearing-reappearing radar chaff to bechemically activated by an oxidizing-reducing agent before dispersalinto the atmosphere and comprising the steps of: applying a layer ofmetallic salt to an electrically inert core, then apply ing a firstlayer of permeable material to the surface of said metallic salt, thenapplying a layer of metallic material to the surface of said first layerof permeable material, and finally applying a second layer of permeablematerial to the surface of said metallic material.

8. The method of producing disappearing-reappearing radar chaff to bechemically activated by an oxidizing-reducing agent before dispersalinto the atmosphere and comprising the steps of: applying a layer ofsilver salt to an electrically inert filament core, then applying afirst layer of resin permeable material to the surface of said silversalt, then applying a layer of metallic material to the surface of saidfirst layer of resin permeable material, and finally applying a secondlayer of resin permeable material to the surface of said metallicmaterial.

2. Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of metallic salt about said core, one or morecoaxial layers of metallic material alternatly spaced with said layersof metallic salt, said metallic salt being reducible by said agent andsaid metallic material being oxidizable by said agent, and a pluralityof coaxial layers of permeable material one of which is between eachlayer of metallic salt and metallic material and one of which forms theouter layer of the chaff so formed.
 3. Disappearing-reappearing radarchaff chemically activatable by an oxidizing-reducing agent andcomprising: an electrically inert core, one or more coaxial layers ofmetallic salt about said core and having the inner layer joined to saidcore, one or more coaxial layers of metallic material alternately spacedwith said layers of metallic salt, said metallic salt being reducible bysaid agent and said metallic material being oxidizable by said agent,and a plurality of coaxial layers of permeable material one of which isbetween each layer of metallic salt and metallic material and one ofwhich forms the outer layer of the chaff so formed. 4.Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert core, oneor more coaxial layers of silver salt about said core, one or morecoaxial layers of metallic material alternately spaced with said layersof silver salt, said silver salt being reducible by said agent and saidmetallic material being oxidizable by said agent, and a plurality ofcoaxial layers of resin permeable material one of which is between eachlayer of silver salt and metallic material and one of which forms theouter layer of the chaff so formed.
 5. Disappearing-reappearing radarchaff chemically activatable by an oxidizing-reducing agent andcomprising: an electrically inert core, one or more coaxial layers ofsilver salt about said core and having the inner layer joined to saidcore, one or more coaxial layers of metallic material alternately spacedwith said layers of silver salt, said silver salt being reducible bysaid agent and said metallic material being oxidizable by said agent,and a plurality of coaxial layers of resin permeable material one ofwhich is between each layer of silver salt and metallic material and oneof which forms the outer layer of the chaff so formed. 6.Disappearing-reappearing radar chaff chemically activatable by anoxidizing-reducing agent and comprising: an electrically inert filamentcore, a layer of silver salt coaxial with and joined to the surface ofsaid core, a first coaxial layer of resin permeable material joined tothe surface of said layer of silver salt, a coaxial layer of metallicmaterial joined to the surface of said first layer of resin permeablematerial, and a second coaxial layer of resin permeable material joinedto the surface of said layer of metallic material, said silver saltbeing reducible by said agent and said metallic material beingoxidizable by said agent.
 7. The method of producingdisappearing-reappearing radar chaff to be chemically activated by anoxidizing-reducing agent before dispersal into the atmosphere andcomprising the steps of: applying a layer of metallic salt to anelectrically inert core, then applying a first layer of permeablematerial to the surface of said metallic salt, then applying a layer ofmetallic material to the surface of said first layer of permeablematerial, and finally applying a second layer of permeable material tothe surface of said metallic material.
 8. The method of producingdisappearing-reappearing radar chaff to be chemically activated by anoxidizing-reducing agent before dispersal into the atmosphere andcomprising the steps of: applying a layer of silver salt to anelectrically inert filament core, then applying a first layer of resinpermeable material to the surface of said silver salt, then applying alayer of metallic material to the surface of said first layer of resinpermeable material, and finally applying a second layer of resinpermeable material to the surface of said metallic material.